$4.5 \mathrm{~g}$ of aluminium (at mass $27 \mathrm{amu}$ ) is deposited at cathode from $\mathrm{Al}^{3+}$…
$4.5 \mathrm{~g}$ of aluminium (at mass $27 \mathrm{amu}$ ) is deposited at cathode from $\mathrm{Al}^{3+}$ solution by a certain quality of electric charge. The volume of hydrogen produced at STP from $\mathrm{H}^{+}$ions in solution by the same quantity of electric charge will be:
$44.8 \mathrm{~L}$
$22.4 \mathrm{~L}$
$11.2 \mathrm{~L}$
$5.6 \mathrm{~L}$
Solution
We know that,
I Faraday charge liberates 1 eq. of substance.
eq. wt. of $\mathrm{AI}=\frac{\text { wt.of } \mathrm{Al}}{\text { eq. } w t}=\frac{4.5}{9}=0.5$
no. of Faraday required $=0.5$
no. of eq. of $\mathrm{H}_2$ produce $=0.5$ eq.
Volume occupied by 1 eq. of $\mathrm{H}_2=$ $\frac{22.4}{2}=11.2$
Volume occupied by $0.5 \mathrm{eq}=11.2 \times$ 0.5
$=5.6$ litre at STP